My zipper wasn`t long enough, so first of all, I cut two small gusset parts for the ends and attached them to it. Then I took the two long gusset parts of fabric and two of the lining, and attached them to the zipper like if you were making a lined zippered pouch. At the very last step of the bag, after putting the lining and the mainfabric together, I attached the lining-gusset parts to the lining and the fabric to the fabric. Very important to leave a small hole somewhere in the lining for turning around afterwards - and to keep the zipper open.